MORPHOFUNCTIONAL ORGANIZATION OF THE VASCULAR BED OF THE LIVER AND FEATURES OF THE NUCLEAR APPARATUS

UDC 61

 

MORPHOFUNCTIONAL ORGANIZATION OF THE VASCULAR BED

OF THE LIVER AND FEATURES OF THE NUCLEAR APPARATUS

 

N.Z. Isayeva, Senior Lecturer

Tashkent Pediatric Medical Institute

(100140, Uzbekistan, Tashkent, st. Bogishamol, 223)

Email: lola.karatayeva@bk.ru

 

J.Sh. Khikmatov, Student

Tashkent Pediatric Medical Institute

(100140, Uzbekistan, Tashkent, st. Bogishamol, 223)

Email: lola.karatayeva@bk.ru

 

Abstract. One of the main criteria for the gradient in the liver are the zones where mitosis is carried out, followed by the movement of cells to the zone of their natural death by apoptosis or extrusion. In this regard, the purpose of this work was to analyze the structure of the hepatic lobule for the presence of a topographic area in it, where liver cells mainly divide, and then, differentiating, specialize to perform certain functions, after which they undergo natural, as is commonly believed, programmed death. However, data on hepatocyte apoptosis are very few, which is obviously due to the difficulty of detecting it at the light-optical level.

Keywords: liver, hepatocyte, mitosis, apoptosis, extrusion, gradient.

 

Materials and methods of research. The material was the liver of mature rabbits (n = 36) of both sexes weighing 2.5-3 kg, kept under normal vivarium conditions. Animals in compliance with ethical standards were slaughtered under light ether anesthesia by decapitation. Pieces of liver tissue for histological studies after fixation and treatment were poured into paraffin. Sections for light-optical studies were stained with hematoxylin – eosin and then viewed under an immersion lens (x100) of a Leitz Biomed microscope (Leica), with a digital photo attachment. For electron microscopic studies, liver tissue was examined under a JEM-100S microscope after appropriate treatment.

Results of research: Morphological studies have established that in the liver of rabbits, as well as other mammals, the main structural and functional element of the organ is the classical hepatic lobule, in the center of which there is a central vein, and on the periphery or border of the lobules there is a portal tract containing the liver triad. The main element of the liver is hepatocytes, embedded in one or two rows and form a hepatic plate connecting the portal tract with the central vein. At this site, each cell is washed with flowing blood through the space of the Disse located between the endothelium and hepatocytes. A detailed and thorough analysis of the state of the cells allowed us to establish that there are very few dividing and dying cells in the lobule. Mitotic division is rare, in our studies it is equal to 1:2500 and were localized in the periportal zones, which suggests the existence of less differentiated cells in this zone. In contrast, the extruded and apoptotically dead cells are mainly localized in the perivenous, occasionally in the intermediate zones of the lobule. The count of hepatocytes forming the porto-venous gradient averages from 15 to 24 cells. The study of the structural organization and analysis of the state of these cells allowed us to establish that cells from the terminally located first 3 rows undergo extrusion, while apoptotic decay is from the perivenous, to about the 8-10 position of cells in the port-venous gradient. As our research has shown, individual cells from the composition of the hepatic plate are usually subjected to apoptosis, which is easy to distinguish from others, due to the enlightened cytoplasm, as well as the swollen nucleus. In such a cell, although the karyoplasm looks enlightened, and chromatin residues are concentrated in the form of lumps, the nucleolus does not stand out, but intercellular contacts with surrounding cells have not yet been disrupted (Fig. 1a). At the next stage of apoptosis, the cell nucleus begins to shrink, chromatin lumps concentrate under the nuclear envelope, and the cytoplasm enlightenment acquires the character of small vacuoles, more precisely vesicles (Fig. 1b).

 

 

Fig. 1. Here and further (in all figures) rabbit liver.

Staining with hematoxylin-eosin.Ok. 15.Volume 100 (immersion). Sequential changes in hepatocytes during apoptosis.

A-enlightenment of the cytoplasm and swelling of the nucleus. B-cytoplasmic vesiculation and decrease in the volume of the nucleus

 

 

Fig. 2. The final stages of apoptosis in hepatocytes.

A-the birth and death of a cell are close. At the top of the picture, pyknosis and fusion of two nuclei of an apoptotic cell,

at the bottom of the picture, mitotic division is visible. B-pyknosis and decay of nuclear contents into lumpy elements

 

It should be noted that in some cases, along with the enlightenment of the cytoplasm, we noted its densification, obviously characterizing the initial stage of apoptosis. Both mononuclear and binuclear cells can undergo apoptosis.

These changes are accompanied by an increase in the enlightenment of the cytoplasm, which is replaced by its lumpy or filamentous decay, however, the cell itself is still part of the hepatic plate. In some cases, when binuclear cells undergo apoptosis, the contents of both nuclei merge, representing a large conglomerate (Fig. 2a). The formation of denser and shapeless core condensates is clearly visible in Fig. 2b. Consequently, the nucleus and cytoplasm of the hepatocyte are gradually completely disorganized, the nucleus takes the form of a compacted mass, and filamentous or granular structures begin to loosen in the cytoplasm

At the final stage of apoptosis, the loosened cytoplasm ruptures and the contents of the cell are washed out into the lumen of the sinusoid, and neighboring cells, shifting, restore the normal architectonics of the hepatic plate. Our light-optical observations are also confirmed by electron microscopic studies, where the cytoplasm of an apoptotically altered cell is also disintegrated and fragmented into apoptotic bodies, among which mitochondria, tubules of the endoplasmic network, as well as lysosomes and phagosomes are barely noticeable.

 

 

Fig. 3. Light-optical picture of hepatocyte extrusion.

A-hepatocyte with an altered cytoplasm and a barely noticeable nucleus crawls out into the lumen of the central vein.

B-homogenization of the cytoplasm of the terminal extruded hepatocyte

 

The cell nucleus is isolated in the form of small lumps of chromatin in the middle of the apoptotic body, fragments of erythrocytes wedged between them, indicate their presence in the lumen of the sinusoid.

It should be emphasized that along with apoptotic death, we have detected the phenomena of extrusion of hepatocytes from the liver plates. In light-optical examination, the extruded cell most often occupies the terminal position of the porto-venous gradient, or is located in close proximity to the perivenous sections of the lobule. Extrusion is characterized by a violation of the contact of cells with others and its movement into the lumen of the sinusoid or central vein. In Fig. 3a, during a light-optical examination, such a cell lies freely in the lumen of the vessel. Moreover, its boundaries are vague, and the nucleus is revealed as a faint shadow, apparently, the cell crawls out into the lumen of the central vein.

Another figure shows the perivenous portion of the lobule (Fig. 3b), where among the group of cells surrounding the central vein, a cell with a weak color or light pink cytoplasm and the absence of a nucleus, but still in contact with neighboring cells, stands out. The morphological picture of extrusion is more clearly revealed during electron microscopic examination. The separated cell has an irregular shape, contains well-preserved subcellular elements, and its poles are easily distinguished. The biliary pole is characterized by the preservation of desmosome residues, as well as the presence of numerous secretory granules, and the sinusoidal pole contains short microvilli and a large number of less modified organelles.

Unlike apoptosis during extrusion, the cell nucleus is swollen, there are no chromatin condensates, however, the structure of the nucleolus, which is small in size and instead of granular-fibrillar elements, is represented by compacted filamentous structures, has been dramatically changed. And finally, a specific sign of extrusion is the direct contact of this cell with intravascularly located erythrocytes and the absence of endothelial lining. The moment of separation of the extruded cell from the neighboring one is shown in Fig. 3, where a fragment of a hepatocyte, still a small part of the cytoplasm, contacts the neighboring one. Moreover, reticular fibers, cellular detritus, as well as contacting macrophage or its fragments from lysosomes and phagosomes are found around this fragment. The presence of an endothelial lining, and fragments of erythrocytes in the lumen of the central vein indicate the process of extrusion of a terminal located hepatocyte.

Discussion of the results obtained.

Morphological analysis of the structure of the hepatic lobule allowed us to deduce single figures of mitotic cell division, mainly in the periportal zones of the hepatic lobule. These results coincide with studies [12], which showed that hepatocyte precursors are localized within a radius of 200 microns from the portal tracts when H3-thymidine is administered. Therefore, it can be assumed that a proliferon is formed in this zone, which differentiates and moves towards the central vein. Topographic analysis of the death of individual, randomly located hepatocytes shows that the cells of the intermediate and central zone of the hepatic lobule undergo apoptosis. The data obtained coincide with studies [4, 5], which also described the apoptosis of the most recent 2 rows of hepatocytes located around the terminal hepatic venule and occasionally between 3-5 rows. In the development of apoptosis, we found 4 consecutive stages: cytoplasmic enlightenment and swelling of the nucleus, cytoplasmic vesiculation and pyknosis of the nucleus, cytoplasmic destruction and nuclear decay, and finally, the elimination of cellular detritus into the lumen of the vessel. The first signs of apoptosis and extrusion begin with a change in the nucleolus. If during apoptosis it immediately disappears among the remnants of chromatin nuclei, then during extrusion its structure undergoes profound changes, namely, granular-fibrillar elements turn into compacted filamentous structures. Obviously, the initial changes in the hepatocyte during apoptosis are accompanied by swelling of the nucleus, then rapidly replaced by its densification, probably associated with the action of proteolytic activity of caspase [8]. The swelling of the nucleus is joined by the enlightenment of the cytoplasm, which leads to a lumpy or vesicular decay. In some cases, we noted the cytoplasm compaction, which is probably due not to apoptosis, but to cell necrosis. Other researchers also point to a similar inconsistency [3]. It has been established that the enlightenment or densification of the cytoplasm is caused by a violation of osmotic pressure in the cell associated with a change in the concentration of calcium ions [3, 12]. Electron microscopically, during apoptotic decay, chromatin condensates and subcellular conglomerates surrounded by a membrane are detected in a cell between vesicular elements, which corresponds to the data of a fundamental study of programmed cell death – apoptosis [9]. Some studies indicate that eventually apoptotic bodies are captured by nearby cells or macrophages [2, 7, 13] however, our studies have shown that in the liver they are most often eliminated into the lumen of the sinusoid, and occasionally, if this happens to terminal hepatocytes, they are phagocytized by macrophages. In the liver, along with apoptosis, like the epithelium of other organs, we have discovered the phenomenon of extrusion, in which the cell is completely separated from the liver plates with less altered subcellular structures. It can be assumed that such a cell is a kind of "long-lived" among the other groups of hepatocytes, without disintegrating into apoptosis, is subjected to extrusion. The results of our light-optical and electron microscopic studies confirm the existence of a port-venous gradient in the liver, within which the neoplasm of young and the death of old hepatocytes occurs. At the same time, hepatocytes, together with stromal elements, constantly move from the periportal zones to the perivenous ones, having reached the final goal, namely terminal hepatic venules, undergo extrusion or undergo programmed death along the way. According to the data of [2], hepatocytes from the periportal zone in the direction of the central one move at an average speed of 1.44 microns/ day. According to these researchers, the development cycle of liver cells ranges from 200 days to 1 year [4, 5]. If we take as a basis the average number of cells that make up the length of the porto-venous gradient, then it is equal to 17-18 cells, then the renewal of this complex, respectively, lasts about as many years. This indicates that the liver is a slowly renewing organ, and its cells are "long-lived".

Thus, the conducted studies indicate the existence of a port-venous gradient, in the periportal zone, poorly differentiated cells undergo division, in the course of cell movement towards the central vein, their differentiation and specialization are carried out. Then, after a certain time, as the cells age, they undergo apoptotic death. More persistent centenarians, reaching the perivenous areas, are forced to break away from "life" by extrusion.

 

Conclusions:

• there is a porto-venous gradient in the liver, where cells function from the moment of birth to death, then undergo death along the way.
• cell death occurs in two ways, apoptotically – by disintegration as part of the hepatic plate, and terminal hepatocytes are more often subjected to extrusion, followed by their elimination into the bloodstream.
• apoptosis in hepatocytes begins with a change in the nucleolus, then captures the nucleus and cytoplasm, eventually culminates in the complete disintegration of the cell with the elimination of cellular detritus into the lumen of the vessel.

 

REFERENCES

1. Arber, N., Zajicek G., Arnicl J. The streaming liver // Liver. 1988. No 8. Pp. 80-87.
2. Aruin, L.I. Apoptosis and liver pathology. // Ross. zh. Gastroenterol. hepatol. Coloproctol. 1998. No 2. Pp. 6-10.
3. Belushkina, I.I. Molecular foundations of apoptosis pathology. // Arch pat. 2001. Vol. 63. No. 1. Pp. 51-60.
4. Benedetti, A.,Jezugel A.M.,Oriondi F. Preferential distribution of apoptotic bodies in acinar zone 3 of normal human and rat liver // J. Hepatol. 1988. No 7. Pp. 319-324.
5. Cande, C., Cecconi F., Dessen P. Apoptosis-inducing factor: key to the conserved caspase- independent pathways of cell death? // Cell Sci. 2002. V. 115. Pp. 4727-4734.
6. Colombono, A., Ledda-Columbano G.M. Com G. et al. Occurrence of cell death (apoptosis) during the involution of liver hyperplasia // Lab. Invest. 1985.No 51. Pp. 670-675.
7. Gryazin, A.E., Bueverov A.O., Ivashkin V.T. Apoptosis of peripheral blood mononuclears in chronic hepatitis C and viral-alcoholic hepatitis // Ross. zh. gastroeterol. hepatol. Coloproctol. 2005. Vol. 15. No. 4. Pp. 35-40.
8. Kerr, J.F.R., Willie A.H., Carrie A.R. Apoptosis: a basic biological phenomen with wid-ringing implications tissue kinetics // Brit. J. Cancer. 1972. No 26. Pp. 239-257.
9. Natozi, S. Hepatocyte apoptosis is a pathologic feature of human alcoholic hepatitis // J. Hepatol. 2001. V. 34. Pp. 248-258.
10. Sadriddinov, A.F. The significance of the nucleolus in the relationship of polyplody and multinucleation of liver cells. "Austrian Journal of Technical and Natural Sciences", January-February. 2014. No. 2. Pp. 64-73.
11. Sadriddinov, A.F., Isaeva N.Z.. The porto-venous gradient is a functional element of the liver. In the collection of the mat-s: International correspondence scientific and practical conference " Scientific discussion: Questions of medicine". Moscow, 2013. Pp. 57-66.
12. Shamirzaev, N.H. Apoptosis. Medjournal of Uzbekistan. 2002. No. 2-3. Pp. 92-98.
13. Vinogradov, A.A. The effect of doxyrubicin on the processes of apoptosis in liver cells in an experiment // Ukr. zhur. exper. med. 2008. Vol. 9. No. 4. Pp. 59-61.
14. Zalessky, V.N., Velikaya N.V. Mechanisms of apoptosis in liver diseases // Modern prob. toxicology. 2002. No 4. Pp. 27-32.

 

REFERENCES

1. Arber N., Zajicek G., Arnicl J. The streaming liver. Liver. 1988. no 8. pp. 80-87 (In English).
2. Aruin L.I. Apoptosis and liver pathology. Ross. zh. Gastroenterol. hepatol. Coloproctol. 1998. no 2. pp. 6-10 (In English).
3. Belushkina I.I. Molecular foundations of apoptosis pathology. Arch pat. 2001. vol. 63. no. 1. pp. 51-60 (In English).
4. Benedetti A., Jezugel A.M., Oriondi F. Preferential distribution of apoptotic bodies in acinar zone 3 of normal human and rat liver. J. Hepatol. 1988. no 7. pp. 319-324 (In English).
5. Cande C., Cecconi F., Dessen P. Apoptosis-inducing factor: key to the conserved caspase- independent pathways of cell death? Cell Sci. 2002. vol. 115, pp. 4727-4734 (In English).
6. Colombono A., Ledda-Columbano G.M. Com G. et al. Occurrence of cell death (apoptosis) during the involution of liver hyperplasia. Lab. Invest. 1985. no 51. pp. 670-675 (In English).
7. Gryazin A.E., Bueverov A.O., Ivashkin V.T. Apoptosis of peripheral blood mononuclears in chronic hepatitis C and viral-alcoholic hepatitis. Ross. zh. gastroeterol. hepatol. Coloproctol. 2005. vol. 15. no. 4. pp. 35-40 (In English).
8. Kerr J.F.R., Willie A.H., Carrie A.R. Apoptosis: a basic biological phenomen with wid-ringing implications tissue kinetics. Brit. J. Cancer. 1972. no 26. pp. 239-257 (In English).
9. Natozi S. Hepatocyte apoptosis is a pathologic feature of human alcoholic hepatitis. J. Hepatol. 2001. vol. 34. pp. 248-258 (In English).
10. Sadriddinov A.F. The significance of the nucleolus in the relationship of polyplody and multinucleation of liver cells. "Austrian Journal of Technical and Natural Sciences", January-February. 2014. no. 2. pp. 64-73 (In English).
11. Sadriddinov A.F., Isaeva N.Z. The porto-venous gradient is a functional element of the liver. In the collection of the mat-s: International correspondence scientific and practical conference " Scientific discussion: Questions of medicine". Moscow, 2013. Pp. 57-66 (In English).
12. Shamirzaev N.H. Apoptosis. Medjournal of Uzbekistan. 2002, no. 2-3, pp. 92-98 (In English).
13. Vinogradov A.A. The effect of doxyrubicin on the processes of apoptosis in liver cells in an experiment. Ukr. zhur. exper. med. 2008, vol.9, no. 4, pp. 59-61 (In English).
14. Zalessky V.N., Velikaya N.V. Mechanisms of apoptosis in liver diseases. Modern prob. toxicology. 2002. no 4. pp. 27-32 (In English).

 

Материал поступил в редакцию 09.02.23

 

 

МОРФОФУНКЦИОНАЛЬНАЯ ОРГАНИЗАЦИЯ СОСУДИСТОГО

РУСЛА ПЕЧЕНИ И ОСОБЕННОСТИ ЯДЕРНОГО АППАРАТА

 

Н.З. Исаева, старший преподователь

Ташкентский педиатрический медицинский институт

(100140, Узбекистан, г. Ташкент, ул. Богишамол, 223)

Email: lola.karatayeva@bk.ru

 

Ж.Ш. Хикматов, студент

Ташкентский педиатрический медицинский институт

(100140, Узбекистан, г. Ташкент, ул. Богишамол, 223)

Email: lola.karatayeva@bk.ru

 

Аннотация. Одним из главных критериев градиента в печени служат зоны, где осуществляется митоз, с последующим перемещением клеток в зону их естественной гибели путем апоптоза или экструзии. В связи с этим, целью настоящей работы явился анализ структуры печеночной дольки на наличие в ней топографического участка, где печеночные клетки преимущественно делятся, а затем, дифференцируясь, специализируются для выполнения определенных функций, после чего подвергаются естественной, как принято считать, запрограммированной гибели. Однако данные об апоптозе гепатоцитов весьма малочисленны, что очевидно, связано со сложностью его выявления на светооптическом уровне.

Ключевые слова: печень, гепатоцит, митоз, апоптоз, экструзия, градиент.